Using matched copper TEM cells for both sham and
exposed groups, we can detect only modest reporter induction in the latter exposed group (15-20% after 2.5 h at 26 degrees C, rising to approximately 50%
after 20 h). Traceable calibration of our copper TEM cell by the National Physical Laboratory (NPL) reveals significant power loss within the cell (8.5% at
1.0 GHz), accompanied by slight heating of exposed samples ( approximately 0.3 degrees C at 1.0 W). Thus, exposed samples are in fact slightly warmer
(by =0.2 degrees C at 0.5 W) than sham controls.

Following NPL recommendations, our TEM cell design was modified with the aim of reducing both
power loss and consequent heating.

In the modified silver-plated cell, power loss is only 1.5% at 1.0 GHz, and sample warming is reduced to approximately
0.15 degrees C at 1.0 W (i.e., =0.1 degrees C at 0.5 W). Under sham:sham conditions, there is no difference in reporter expression between the modified
silver-plated TEM cell and an unmodified copper cell. However, worms exposed to microwaves (1.0 GHz and 0.5 W) in the silver-plated cell also show no
detectable induction of reporter expression relative to sham controls in the copper cell. Thus, the 20% "microwave induction" observed using two copper
cells may be caused by a small temperature difference between sham and exposed conditions.

In worms incubated for 2.5 h at 26.0, 26.2, and 27.0 degrees
C with no microwave field, there is a consistent and significant increase in reporter expression between 26.0 and 26.2 degrees C (by approximately 20% in
each of the six independent runs), but paradoxically expression levels at 27.0 degrees C are similar to those seen at 26.0 degrees C. This surprising result is
in line with other evidence pointing towards complex regulation of hsp16-1 gene expression across the sub-heat-shock range of 25-27.5 degrees C in C.
elegans.

We conclude that our original interpretation of a non-thermal effect of microwaves cannot be sustained; at least part of the explanation appears to
be thermal.